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Wow! If I had a nickel for every time a Trek show had a blind engineer, I'd have two nickels. Which isn't a lot, but it's weird that it happened twice. Right?
(startrek.website)
Transcription: A side by side picture of Star Trek Strange New Worlds character Hemmer and The Next Generation character Geordi La Forge.
He was just a mycology engineer, not the chief engineer. I honestly can't remember if we ever see main engineering on Discovery. They mostly work in the Spore Drive engine room. But that was Discovery's schtick, that it wasn't the "main" crew that were the stars originally.
But that link literally says he's the chief engineer. I've never actually watched discovery though.
He eventually became chief engineer when Burnham was made captain. He started out just as a regular crew member. None of the main cast were in special positions at the beginning. That was one of the main complaints, because we never learn much about the bridge officers.
He never became Chief Engineer because Stamets was never an Engineering Officer. He's in Science Division. The link is just flat out wrong. I suspect they might be using 'chief' engineer to mean that he's the engineer we see the most of in Season 1. Also that link hasn't been updated since Season 1.